This invention relates to internal combustion engines, and more specifically to internal combustion engines utilizing heat recovery systems to increase engine efficiency.
In a review of internal combustion engines, the gas-fueled Otto engine and the diesel-fueled diesel engine appear to be the only types of engines that have survived the test of time and remain in widespread use.
The diesel engine has a greater thermal efficiency than the Otto engine due to the higher compression ratios of the diesel engines. High compression ratios are employed to achieve high temperatures from the compression.
It is common knowledge that an engine possessing an expansion ratio greater than the compression ratio has a greater work output than a comparable engine where the compression ratio and expansion ratio are the same. In the Otto engine all cylinders have the same swept volume negating the option of increasing the expansion ratio.
It is further recognized that internal combustion engines have low thermal efficiencies due to high heat losses, primarily through the exhaust systems. Other concerns over the internal combustion engine are the desire to reduce harmful exhaust emission and to reduce fuel consumption of engines to protect our problematic crude oil position.
The oil supply for our fuels is not limitless. Once the oil supply is gone, it is gone for good. The worldwide demand for oil continues to increase with no letup in sight. It becomes imperative that we develop more energy efficient devices, including the internal combustion engine. The introduction of the hybrid vehicle system is industry recognition of the need to conserve fuel.
Internal combustion engines are, in reality, heat engines with fuel being the source of the heat. Thermal efficiencies of internal combustion engines are low because much of the heat contained in the fuel ends up as waste heat, either exhaust or coolant losses. Engine manufacturers have made no effort to recover and recycle any of this waste heat.
It is generally accepted by the industry that high compression ratios are the path to improved engine efficiencies. Fuels were developed using high octane and special additives to help retard fuel ignition so that higher compression ratios could be used. Most of the present gas-fueled engines inject the fuel into the intake air supply before compression. High compression temperatures may cause premature air fuel ignition, thus the present limit on compression ratios and compression temperatures.